Express in $kg:-$

$300g$

Conversion of weight:

We know that

$$\begin{gathered} 1kg=1000g \\ \Rightarrow 1g=\frac{1}{1000}kg \end{gathered}$$

so,

$$\begin{gathered} 300g=300\times \frac{1}{1000}kg \\ =\frac{300}{1000}kg \\ =\frac{3}{10}kg \\ =0.3kg \end{gathered}$$

Hence, The required solution is $0.3kg$